High Mass Resolution Multireflection Time-of-Flight Secondary Ion Mass Spectrometer

Abstract

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is popular because of its advantages of parallel <i>m</i>/<i>z</i> detection and less damage for unknown or rare samples compared to sector field instruments. However, the mass resolving power of conventional TOF-SIMS is limited by its relatively large energy spread and primary ion pulse width. In this work, a high mass resolution multireflection time-of-flight secondary ion mass spectrometer (MR-TOF-SIMS) was designed and constructed. Compared with conventional TOF-SIMS, the ion flight path of the MR-TOF-SIMS was extended from meters to subkilometers, and the mass resolving power reached to 87000 after an 80 cycles flight. A pair of symmetrically arranged ion orthogonal injection/ejection deflectors, which could eliminate the influence of fringing field and remove ions with a large energy spread, were proposed to further improve the mass resolving power in fewer flight cycles. A zircon standard sample sputtered by a 10 keV O₂^- beam was used to demonstrate the performance of the MR-TOF-SIMS instrument. As a result, the mass resolving power was up to 30000 only after 22 flight cycles. The ⁹²Zr⁺ peak was significantly separated from the mass interference peaks of ⁹¹ZrH⁺, ⁹⁰ZrH₂⁺, ¹³CC₆H₇⁺, and C₇H₈⁺. The mass accuracies of Zr ions and their hydrides were better than 1.2 ppm. An ion transmission efficiency over 40% was achieved after 115 cycles.